This application claims the priority of German application 196 47 962.2, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for making holes at the circumference of a hollow shape and a device for this purpose.
A method and a device for making holes at the circumference of a hollow shape are known from U.S. Pat. No. 4,989,482. Following a shaping process involving internal high-pressure shaping at an internal pressure in the range of approximately 7 to 700 bars, a hole is produced in the circumference of a hollow shape still in the mold by guiding a punch against the wall of the hollow shape from the outside, said wall being pressed into the interior of the hollow shape by the flush application of the punch. The punch has a channel that connects its face adjacent the hollow shape and is provided with a cavity communicated with the atmosphere. As a result, a pressure differential develops between the end of the punch in the vicinity of the cavity and the interior of the hollow shape, said pressure differential pressing the hollow shape against the annular contact surface of the face of the punch that surrounds the cavity. During further indentation of the wall of the hollow shape, the limit of stretchability of the material of which the hollow shape is composed is reached, and when it is exceeded the wall of the hollow shape tears around the point of impact of the punch to form a slug. Because of the uneven wall of the hole that is produced, however, there is inadequate sealing of the space that is formed as the punch is advanced between the outside of the hollow shape and the female die guiding the punch, and there is no guidance of the punch by the female die relative to the interior of the hollow shape that is pressurized by a fluid, so that despite the radial application of the wall of the hole to the circumference of the punch, a pressure drop occurs within the hollow shape.
As a result, the pressure differential between the atmosphere and the interior at the hollow shape is so low that the suction exerted by the punch on the slug is canceled out, or at least is reduced to a significant degree. In the former case, the slug comes loose from the punch and drops into the interior of the hollow shape. In the latter case, the slug remains adhering with a low force to the end of the punch. During the return movement of the punch, the slug falls back into the hole. However, this occurs only partially since the wall of the hole, which is bent toward the interior of the hollow shape as a result of the return movement of the slug caused by the retraction of the punch, offers a resistance, so that because of the abovementioned low suction force, when the pressure equilibrium is established, the punch lifts away from the slug. In most cases, the slug immediately falls into the interior of the hollow shape without adhering to the wall of the hole. On the other hand, the slug can remain hanging in the hole, so that the clamping effect in the latter is small.
Contrary to the assertion made in the above-mentioned document, it is possible for pressure to build up inside the hollow shape following jamming of the slug, so that the bent wall of the hole is flattened, resulting in an additional clamping of the slug in the hole. No pressure can develop under these conditions because there is no match between the shapes of the wall of the hole and of the slug in the jammed position in which the slug projects into the interior of the hollow shape. This rules out a position of the slug against the wall of the hole that can provide an effective seal against high pressure. Because of the vibrations of the hollow shape that occur as the hollow shape is removed from the internal high-pressure mold, the slug comes loose from its unstable jammed position and drops into the hollow shape. Since the interior of the hollow shape still has a wet film on it despite the fact that the high-pressure fluid has been removed, the slug slides out of the hollow shape when the latter is removed and drops into the mold. Separate removal of the slug from the mold is very awkward, and a slug that has been "forgotten" and is left in the mold can cause irreparable damage to the mold during subsequent shaping processes.
A goal of the invention is to improve a method and a device for making holes at the circumference of a hollow shape such that the slug produced during perforation can be removed in simple fashion from the internal high-pressure mold.
This and other goals have been achieved according to the present invention by providing a method for producing holes at the circumference of a hollow shape, with a wall portion being separated as a slug from a hollow shape within a mold that uses internal high pressure and can be jammed in a previously formed hole without projecting with respect to the outer circumference of the hollow shape, characterized in that the jamming of separated slug with a high fluid pressure that is relaxed relative to a high internal fluid pressure and secured against loss takes place by means of a punch and in that slug, following removal of finished hollow shape from internal high pressure mold, is separated from hollow shape when hole is finally cleared.
This and other goals have been achieved according to the present invention by providing a device for making holes at the circumference of a hollow shape, with a punch integrated into an internal high-pressure mold, by means of which a punched portion of the wall can be separated as a slug from the hollow shape with preliminary production of a hole, and with a return means by means of which the separated slug can be jammed in a hole, and is then jammed in a previously prepared hole without projecting relative to the outer circumference of the hollow shape, characterized in that the return means is a punch with which slug, without fear of loss, in a pressure state that is less than an internal high pressure that is used for internal high-pressure shaping, can be forced inside hollow shape into previously produced hole and in that the device incorporates a means for removing slug following removal of finished hollow shape from internal high-pressure mold, by which hole is finally produced.
According to the invention, the slug can be jammed without the aid of internal high pressure produced by a fluid in a previously produced hole in such fashion that the hollow shape can be removed from the internal high-pressure mold without the slug falling out of the hole in the process. This eliminates the expense of cleaning slugs out of the mold. In addition, there is no need to develop a high fluid pressure or to provide the apparatus associated therewith for pushing the slug back into the hole, and high-pressure-resistant seals can be eliminated as well. Because of the lack of any projection of the slug in the hole above the exterior of the hollow shape, the hollow shape can also simply be removed from the mold. In addition, problems with recovering the slug as far as process engineering is concerned, involving a pressure drop after the hole is made, are overcome. The jammed slug is removed in simple fashion after the hollow shape has been removed from the mold, with the slug not causing any damage or cleanup cost because of its external removal. Because the slug is firmly jammed, perforation at the circumference of the hollow shape is possible at all angles relative to the axial position of the hollow shape inside the mold, without there being any danger, after the pressure is released following production of the hole, of the slug dropping into the hollow shape or, upon removal of the hollow shape, falling into the mold from the inside to the outside after the hollow shape has been removed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.